Gold and silver in whichever form they are in (jewellery, coins, or ingots etc.) are all subject to Zakat.
If you own personal items made from a mixture of metals, then the gold/silver is liable to Zakat if the gold/silver content can be distinguished and ascertained.
Some scholars are of the opinion that mixed metals are only liable to Zakat if half or more of the metal is gold or silver.
Zakat on other metals
There is no Zakat due on platinum and palladium or other precious metals apart from gold and silve